Nonlinear dynamics of two-color optical vortices in lithium niobate crystals

Abstract

We study experimentally the nonlinear dynamics of two-color optical vortex beams in the presence of second-harmonic generation combined with the effects of photo- and thermal refraction, as well as self- and induced-phase modulation. We use an iron-doped lithium niobate crystal as a nonlinear medium for the vortex propagation and observe experimentally, depending on the laser wavelength, a decay of a double-charge vortex, splitting and reshaping of background beam, pattern formation, and controllable nonlinear rotation of a vortex pair.

Dynamics of a paired optical vortex generated by second-harmonic generation

“…One of the major contributions is given by the walk-off of the nonlinear crystal [15,16]. The pump depletion (back conversion from the second-harmonic beam to the fundamental beam) also plays an important role in the SHG pumped by a vortex beam [17]. We neglect this process assuming the SHG with low conversion efficiency.…”

Orbital angular momentum in noncollinear second-harmonic generation by off-axis vortex beams

“…Among nonlinear optical interactions, second harmonic and parametric processes concerning fields carrying optical vortices attracted interest because they grant the possibility of manipulating the dynamics of the phase singularities [11][12][13][14][15][16][17]. This means that, together with the frequency doubling, the SH generated field shows phase defects correlated to the ones present in the pump beam.…”

Management of the orbital angular momentum of vortex beams in a quadratic nonlinear interaction

“…Some of the nonlinear processes which affects the propagation dynamics of optical vortices are parametric frequency conversions in quadratic nonlinear media [15]. Among them, second harmonic generation in a collinear scheme was also copiously studied, using a LG mode as fundamental field (FF) and focusing the attention on the conservation of the orbital angular momentum [17][18][19].…”

“…A variety of interesting effects has been analyzed and observed such as the rising of vortex solitons [13], splitting of solitons [14], and creation and annihilation of vortices due to the interaction of the singularities in nonlinear media by means of the dislocations' dynamics [10,12]. Some of the nonlinear processes which affects the propagation dynamics of optical vortices are parametric frequency conversions in quadratic nonlinear media [15]. Among them, second harmonic generation in a collinear scheme was also copiously studied, using a LG mode as fundamental field (FF) and focusing the attention on the conservation of the orbital angular momentum [17][18][19].…”